Electronic code-typewritter system



Dec. 8, 1953 N. G. A. DoRr-'MAN ELECTRONIC CODE-TYPEWRITER SYSTEM 4 Sheets-Sheet l Filed April 16, 1952 N GA. DORFMAN INVENToR.

lr o at Dec. 8, 1953 N. G. A. DORFMANY 2,662,112

ELECTRONIC CODE-TYPEWRITER SYSTEM Filed April 16, 1952 4 Sheel3S-Sheet 2 FI G l INVENToR.

M a. A. aoRFMA/v Dec. 8, 1953 N. G. A. DoRFMAN ELECTRONIC CODE-TYPEWRITER SYSTEM 4 Sheets-Sheet 5 Filed April 16, 1952 Ss lal MGA. oom-'MN INVENTOR.

BY @wgmi N. G. A. DORFMAN ELECTRONIC CODELTYPEWRITER SYSTEM Dec. 8, 1953 4 Sheets-Sheet 4 Filed April 16, 1952 N. 6.A. DOR/MAN INVENTOR Patented Dec. 8, 1953 delimita Af'isrii is, 1952; siial Nei; 232,565 '2, dans, (ci. iis-siii The present invention is concerned with` improvements inthe art' of code communication and particularly with respect to'. devicesr for facilitatingand improving the quality and ease of such communication.V A l The advantages of code,v communication over direct* voice communication, particularly with respect to reliability of 'transmission of intelligence, are Weill known. However, one' of the factors which has prevented the utilization of codeA conimunication to its -ful'lest extent has been the erraticv production. of code characters Y necessarily implicit in manual sending due toV such factors as operator fatigue or lack of skill, and limitations on the speed .of transmission, which is generally slower thanlspeedsof receptiono'f whichordinary operators are capable.` additiomeach operator has personal idiosyncrasies of sending individual to himself which in many instances permit recognition y of the operator by these characteristics, termed ,signature Y `I n order to avoid some of the disadvantages or drawbacks' implicit in such manual communica'- tiomrecourse has beenl had to automatic systems.

AWhile tl'ie long establishedV system of code .com-

niupiation has been the International Morse code, it hasgbeen found that the International Morse code, by virtue of the haphazardmanner in which -it was originated; is not'adapted to .efficient automatic communication, and,` as a result, substantially all automatic codecommunication systems have devised specialcode arrangements, of which" a common example is the tel'etypewriter code, which are required for efcient utilization of automatic devices' for code' communication. However, such automatic systems reduire special receiving machines' in additionv to special sending machines,V and reception cannot. be interpretedby an operator directly and audibly.

Thegniost desirable solution toy theseproblems would be an apparatus which would produce" uniform, high quality, code characters utilizing' a minimum of manipulative skill' at thev transmit'.- ting-end and inaioodewhich could be' received diretly and'audiblyby operators withoutirequiriing any special receiver apparatus'other than'the conventionalcode receiver now in customary use. It `would `further be desirable tov` provide" such a transmitting apparatus; with a: greater speed'f of transmission than v can be; readily obtained man-- sally, Yexcept by the most highly skined and exz- The present inventionaccomplishes these purposes and supplies a machinell'aving a typewriter keyboard operated` exactly the same as a type'- writer, and which-produceselectrical code signals suitable for transmission dra receiver in any known manner, suoli alsfby' direct wire or carrier modulation, either by, wire or radio rink;

According. to, the4 present invention any desired eodemay' be diinzed; Iii thefoiiowiag detailed descriptioiiof the' presetinveiitiori, @geinteresti-onal Morse code is used byway or ample, siii-ce ii is prop-amy die mdsrcciiipiidated'br ihe code systems which' have' been suggested for use. The principles gf ige esenti invention, "however, are equally applicable' to any type of code arrangement, and practicallyanyother system suggestedwillzo'ier lessr complication and be' a simpliication v.of .the apparatus herein disclosed.

Y, 1rIjhe"presentinyention particularly pertains to improved methods and apparatus forradio. and

wireY Aoolrmrlimmation and'fJnor-e particularly to methods and apparatus for forming electrical .code signais by electronicmeans operating re- Spouse to .a keyboardwhich mayzbe similar to that of a standard. printing typewriter. `The electricalv Vs ignalsthus produced maybe usedin any desired manner and,;for, example, may be substituted forrrthe' signals created'by standard. hand operated telegraph key tolse subsequently transmtted to' a-receiving'V station in any desired'l manner.

A particular advantage of thepresent system resides in an extremely simple` adjustment for the Speeder transmission permitting setting the basic timingrate, .to anyvk desired Vvalue between low and high'extremes of the order off 5 to 125 words per Y minute;

When-applied to Morse code;whose `vcode chainacters are made of dots;v dashes and spaces, ,v'vithM dots' and spaces-lof'equa'l; duration and dashesgof ltl'iree times that duration, thei present invention ofersextreme simplicity in usingfwhat I; term' the Series Sequence'fSystem,iwhich `does not requireseparategeneration;of dot signals', space signais and dasnsignalszplus provision for intermiX-ing these signals; Acc(liirding:` to. .l the present invention:aY single sequence of )uniform duration pulses is/prodiiced for each*v character, with..v an .overail sequence length .coordinateri to the length of the character being sent, and dots, .Sloeries 1 anddas'hes are' `formed inproper number and" sequence by, controlling in simple; manner the passagezor blookingrof"` the'ipulses of that se.- duence. The numberof puises" require'd in the Ssdllllcl and .lijheblooking or.v .passing ofA appro;- priate pulses to form the desired character, are

.'1 and 19 unit intervals. ation in theduration of code characters, it is not 3 performed automatically merely upon depressing the keyboard key corresponding to such desired character.

These and other features are made possible by the use of special principles and apparatus forming the present invention, other objects and advantages of which will become more fully apparent from consideration of the following detailed description of an illustrative embodiment thereof, taken in conjunction with the appended drawings, in which:

Figure 1 is a schematic block diagram of the entire system embodying the present invention;

Figure 2 is a chart of the Morse code arranged with all characters terminating to show the principles of the invention;

Figure 3 is a fragmentary schematic circuit diagram showing portions of the unit interval generator chain, the keyer section, the sequence selector section, and the eraser and monitor sections of the present invention;

Figure 4 is a fragmentary circuit diagram of portions of the keyboard and phantom switch network of the present invention.

Basic principles Before describing in detail the apparatus illustrating the present invention, a brief discussion will be given of its basic principles. The International Morse code as is well known, consists of L some 43 different sequences of dots and/or dashes in different combinations, each combination representing a character, such as a digit o1' a letter of the alphabet, or punctuation mark, or a special code symbol, such as BT, AR, AS or SK, each such character having its individual code representation in dots and dashes. The interval forming the dash is by standard convention three times the time interval forming a dot. Also, the spacing between two successive dots or dashes of the same character is standardized as equal to the time interval of one dot.

A basic principle of the present invention is the use of the dot (or space) duration as a unit time interval with respect to which all time relations are coordinated. Since the dash interval is also coordinated to and based upon this unit interval, the total time duration of any particular character is solely dependent upon the unit interval. As one important feature of the invention, described in detail below, the unit interval is made adjustable very simply, thus rendering the speed of transmission adjustable at will.

.In the Morse code the total duration of code character, as measured in unit intervals, varies `from one unit interval for the letter E, whose code symbol is a single dot, to 19 unit intervals for the digit zero (whose code character is iive dashes with four spaces) and for the comma (two dashes, two dots, two dashes with six spaces). Other characters have varying durations between Because of this varipracticable to devote a constant time interval to each character, since that would waste a considerable portion of the interval for the shorter characters. It is then necessary that the characters be allotted varying time intervals corresponding to the number of unit intervals involved in each.

This is readily accomplished in the present system, by the selection of the end of each character as a reference datum, and controlling the instant of commencement of the characters in accordance with the number of intervals it has.

This is illustrated in Figure 2, which shows the Morse code in terms of the unit intervals, with all characters terminating with interval 19. It will be seen that the nature of this code makes all characters have an odd number of unit intervals, and all characters start at the beginning of the odd-numbered unit intervals, with all odd unit intervals thereafter being marks (that is, dot or portions of dashes) Also, all spaces fall into the even-numbered unit intervals, but not al1 such even unit intervals are spaces, some being marks, such as interval 18 in the letter A.

While the present invention is capable of use with any general code system, the above characteristics permit some simplifications when using Morse code. rihus, after the initiation of a code charactervis accomplished after proper interval number, it is necessary to control only the even-numbered intervals therebeyond, as to being a space or a mark, in order to form the proper code character.

The present system produces an output signal represented by the opening and closing of a pair of contacts of a keying relay, corresponding exactly to the opening and closing of a manual telegraph key, to produce marks during closed through its winding and having a pulsed wave form corresponding to the output signal, with short (unit interval) pulses for dot marks and long (3-unit) pulses for dash marks.

To provide the Varying combinations of dot pulses, dash pulses and spaces, the present system has a generator section which for each character to be transmitted produces a number of uniformduration electrical pulses equal to the number of unit intervals in that character. These pulses 4are supplied to a keyer section which is controlled so as to pass to the output keyer relay only those pulses required to make up the marks vfor the character, a dot mark being formed by a single pulse and a dash mark being formed by three successive pulses. The keyer section is controlled by a sequence selector section which '1n turn is operated by a keyboard through a special phantom-switch network.

The general System As shown in Fig. 1, the system comprises a chain of cascaded unit interval generators UIGI, UIG2, etc., equal in number to the largest number of unit intervals in the code system employed, being 19 in Morse code. These 19 generators UIG! to UIGi 9 are connected in a cascaded chain Morse code characters plus a clear or checking key CL. Upon depressing one of these keys, a trigger pulse is supplied to the generator chain,

Vat a point such that there are as many unit interval generators following that point as there are unit intervals-in the code character repre- `l sented by the depressed key. 'I'he generator chain then produces a sequence of successive uniformduration rectangular pulses equalv in number to theY unit intervals inthe code character;

Each of the unitinterval generators UIGI to -UIGIB is coupledV to a respective keyer Kl to KIS. Each ofthe even keyers is a gated tube, controlled by a respective sequence selector SSZ -to SS'l'8 (in Morse code, thev odd keyers Kl, K3, etc. do not have to be gated, and their corresponding sequence selectors SS l, SSB, etc., have therefore been omitted from Fig. 1). All the `keyers arevcoupled in parallel to a common-keying relayKR, which closes its contacts when- -ever any keyerpasses a pulseA to the relay winding.

Each keyer determines whether or not the pulse produced by its corresponding generator shall pass to the output keying relay to produce a mark or shall be blockedY to form a space. As indicated above, all pulsesn in odd-numbered vintervals after initiation of the character are marks, so that the odd-numbered keyers need not be controlled, but are permanently conditioned to pass the pulses on to the keying relay. vThe even-numbered keyers are normally blocked, `and would therefore form spaces in the trans-'- mitted code character.

To form a dash, an even-numbered keyer is conditioned or gated to pass its pulse,V whereby three successive generator pulses are permitted to pass to the relay KR, forming a dash. The,

etc., to determine whether they shall pass or block their pulses. TheV depressed key of the keyboard KB determines appropriately which of the sequence selectors is to be triggered, togate on the corresponding keyers, so as to form dashes in the proper relative positions in thecode char.- acter. The phantom-switch network PS provides theproper connections between the keyboard KB and both the sequence selectors SS and the unit interval generators UIG to carry out these functions.y

In addition to these sectionsv ofthe system, several special purpose sections are included. The eraser circuit E provides forY reconditioning the sequence selectors after each character, to make them properly receptive to the depressing of a key for the next character. The monitor circuit M permits the operator, to listen to his ownY transmission, either asa check on his sending or to assist in learning code. The speed control SC adjusts the duration; of all the unit interval pulses simultaneously, thereby adjusting the time durationfof each lcharacter and permitting adjustment of the speed of transmission between wide limits, such as 5 to 125 words per minute.

The specic. functioning of each of the abovementionedportions of. the presentv system will become more clearly apparent fromv the following detailed description thereof.

The unit yinterval generator chain The specific circuit details of the unit interval generator chain will beseen in Figure 3, which yshows a circuit diagram of the portion of the system of Figure 1, including the unit interval generators -UIG-Ia and UIGI9, the keyers KI8 andLKIS., the sequence selectors SS I-8, the `eraser circuit, E, the monitor circuit S and the speed control SC'.

All` .thegunit interval generators' -UICSfI to t9 have exactly the same circuit. which is exemplined bythe circuiti of generator I8, shownY 3.. The generator is formed by a pair of tube sections 2l and 22 which are. preferably the two sections of a dual tube, although separate tubes may be used where desired. These tube sections 2| and 22 are illustrated as being. triodes. such as.- of the 6J6 type, which have. been found to be highly satisfactory, although multigri'd tubes may be utilized where desired. The anode of the first tube section 2l is coupled tor a source of' positive potential 23 serving as a4 common plate supply for all generators, by' way'of a load resistor R202. Similarly, the anode of the second tube section 22 is coupled to the source 23` through its load resistor R203. The cathodes of both tube sections are connected together and through a common cathode resistor R204 to the common negative terminal 24 of the positive potential source Y23; this terminal 24 may be at ground or chassis potential.

The first section grid is connected to the negative terminal I4 through a gridv leak resistor R201. The second section grid is connected through a grid leak resistor R205'to a reference voltage lead 2E common to all generators connected to the variable tap 21' of the speed control potentiometer SC which has one end connected to the negative terminal 24 and the other end connected to the positive potential source 23, whereby the potential of lead may be adjustably set to a positive value'less than that of the plate voltage source 23'. The first section anode is coupled by a condenser C292 to the second section grid. The interconnected cathodes of the two tube `sections are coupled through a condenser C201 to the first' section grid of the following generator in the chain.

The generator has an input lead 28V supplied from the trigger pulse output from the preceding generator, and which triggers the generator at the end of the unit interyalpulse of the preceding generator. Also, as indicated above, it is desired to initiate operation ofthe generator chain at various pointsr to. produce unit interval pulse sequences of different lengths corresponding to the lengths of thevarious characters. The first generator UIG'I is triggered'ol by supplying asuitable trigger pulse to its lead` 28 from the keyboard and phantom-switch network as described below. Intermediate generators .could be triggered similarly by such trigger pulses applied to their leads 28,. However, it is .desirable to have a low impedance input coupling for such trigger pulses, and hence such pulses are applied in the present. circuit .to lead 2.9., .which is converted to the cathodes of. the generator tbe.- fore the one to be triggered, Yand is then transferred through coupling C2'0I`, R261' to the grid of the generator to be triggered. For Morse code, only the odd-numbered generators need ybe triggered, and hence. leads .2S are used only with theprecedingeVen-numbered.generators and `are omitted from the. rest.

The generator alsohas two. outputs, namely, lead 3l going lto lthe first section grid foi the following generator, and lead vv32--coupledto the right section anode,.and going through v,anisola-.ihing andV grid-current-limiting resistors-R335 die the keyer Kw .corresponding-,togenerator le, the `keyer circuit being rdescribed fbelow.

The operation of the unit linternal generator chain is as follows:

In the quiescent condition, Iall the grst tube sections fare biased beyond ,cut-on by zthev .volte drops in the :.cathoderesistors :R2i!,4. 'hfaaio'siVF tive pulse is applied even momentarily to the left section grid of generator I, it serves to render the left section conductive, and current flows through its load resistor R202, which depresses the potential of the left section anode. This change in potential is transferred through condenser C292 to the right section grid, driving the right section to the plate current cut-off, raising the potential of the right section anode. The length of time that the right section will remain cut on is dependent upon the time of constant of the condenser C202 and resistor R295 and upon the reference voltage appearing on lead 26. After this time interval, the right section begins to conduct, which increases the cathode potential and cuts off the left section, which action cumulatively unblocks the right section, causing an abrupt decrease in the anode potential of the right section, terminating the generation of a single positive rectangular pulse at the right anode, which pulse is a unit interval pulse and is supplied to the corresponding keyer input by lead 32.

Coincident with the termination (trailing edge) of this pulse, the voltage across cathode resistor R292 rises and a positive pulse is supplied through condenser C291 and resistor B2b! to the left section grid of the following generator. This positive pulse serves to initiate the same cycle of operations in generator 2, which accordingly produces two similar output pulses, namely, a unit interval pulse fed by lead 32 to the corresponding keyer, and a short-duration pulse coincident with the termination of the unit interval pulse which is supplied to the input of the following generator to repeat the same cycle which is repeated in turn by each generator in the chain.

In this way, if the initiating pulse is supplied to the input of generator l, the unit interval generator chain automatically generates 19 successive unit interval pulses, each supplied to a respective keyer. Where less than 19 pulses are required (for characters having fewer than 19 unit intervals) the initiating pulse is supplied to the lead 29 of the appropriate generator. The initiating pulse is thereby fed by condenser 029| to the input of the succeeding generator to commence the sequence of unit interval pulses at that point. For example, if but one unit interval pulse is desired (as for letter E), the initiating pulse is supplied to lead 29 of generator i3, so

that only generator i9 is triggered. 1f the initiating pulse is supplied to an intermediate generator, such as, for example, to the cathodes of generator No. l0, then only generators li to i9, inclusive, produce the sequence of unit interval pulses, now 9 in number, suitable for a code character having a duration of 9 unit intervals.

The speed control The control of the duration of the rectangular pulse produced by each generator and supplied to the keyer, that duration being the unit interval, is dependent upon the reference voltage on lead 26, which in turn is regulated by the speed control potentiometer SC. Since this potentiometer SC adjusts the reference voltage for all of the right section grids of all of the generators simultaneously, it will be seen that it simultaneously varies the unit interval for all 19 intervals, and thereby varies the duration of all of the code characters in equal ratio. This is, accordingly, a simple and convenient speed control which can determine how many characters or words per minute can be transmitted by the apparatus Without overlap of output code signals.

Gil

The keyer section The keyer section of the present system is comprised of 19 keyer circuits KI to KIS. In the present instance, these are illustrated as triode tube sections 30 and again may be sections of a dual tube or independent tubes. Types 6J6 tubes have been found satisfactory. Alternatively, multigrid tubes may be used Where desired.

Each of the keyer tubes 30 has its input grid coupled to the unit interval pulse output of a corresponding unit interval generator, through a respective isolating and grid-current-limiting resistor R396. The cathodes of all the keyer tubes 30 are directly connected together and to one terminal of the winding of the keying relay KR. The other terminal of this relay winding is connected to a source of low positive potential which may be obtained for example, by means of a voltage divider formed by resistors R123 and R124 connected between a source of high positive voltage 33 and the common negative terminal 24. This low positive potential thus derived is chosen to have a value which, in the absence of signal input to the keyer grid, maintains all the keyer plate currents cut off, so that no current iioWs through the keying relay KR.. However, when a positive unit interval pulse is derived from any one of the unit interval generators and is applied to the corresponding keyer input grid (and provided that the anode of the keyer 3i) in question is coupled to the positive potential source 33 as described below) the keyer tube 39 Will conduct during the application of the unit interval pulse thereto, which will cause current to ow for that interval in the winding of keying relay KR, which will close its contacts for that interval to produce a corresponding output pulse.

To control which or" the keyers will pass its input pulses and which will remain blocked, so as to form the desired code characters, the anode voltages of the keyers are gated by the sequence selectors, as described hereinbelow. However, as mentioned above, there is no need to control the odd-numbered keyers, since all the odd-numbered intervals beginning with the rst odd interval utilized, are mark intervals. Therefore, each of the odd-nurnbered keyers has its anode connected directly to the positive potential source 33, as is illustrated with respect to lieyer Kl9 in Figure 3. However, depending upon the particular code character being transmitted, certain of the evennumbered keyers are required to remain blocked to prohibit passage of a unit interval pulse therethrough, to form a spacing interval, while others may be required to be unblocked to cause an even marking interval which cooperates with the adjoining odd marking intervals to form a dash. The even keyers must therefore be gated in a manner corresponding to which code character is being transmitted. This gating is performed by the respective sequence selectors, of which only the even-numbered ones are required in the case of International Morse code. It will be understood that, in the case of other codes, some or all of the odd-numbered sequence selectors may be necessary.

The sequence selector section Figure 3 also illustrates the circuit diagram of one sequence selector S553, the circuit diagram for the others being' identical thereto. The sequence selector is formed by a grid-controlled gas discharge tube 313, such as a 2D2i thyratron. The anode of selector tube 34 is coupled through a load resistor R4H to a lead 2| and thence 19 .through the .normallyllosed contacts ,38 of the eraser .rlayER .tobe describedftofthe .source 33 Vdi. .high :positive potential. The js'cr'e'en gridof 'ruhe :34 is .connected Lto the vsource '33 through resistonRZilfB :andiis also connected tothe cathode, .Wh'ich'in turnis connected to-the 'negative terninal '2li through a resistor R412. ``The 'input vgrid connected through .-a gridleak resistor 'Rto V`negative 'terminal "2t, .and 'has Tan inputlead 346.

The cathode oi" 'tube '3'13 is also connected tothe Aanode of the corresponding .keyer tube `30 by 4a 'lead 35.

It will thus be seen that, solong as tube 34 rev mains non-conductive,.thepotential of theanode .of the keyer tube .Bis determined Iby the voltage divider formed by resistors R4`l'3 and R4'I2. Theseresistors are so chosen -that the keyer -ltu'be has .insufficient anode voltage to conduct and v.remains blocked despite application of .a positive .potential to its grid. However, when sequence selector tube 3 becomes conductive, Yit Adraws current from .the source 3'3 .through contacts v`22, lead f2! and resistor R4H, which current also flows 'throu'zh cathode .resistor R'iiflZ and raises '.theivoltage thereacross, whereby theanodepo'tential of the keyer tube 30 is raised-toa value su'iiicient to gate on the .keyer .tube 131) and condition .it .to become conductive upon application'of a unit kinter-val pulse to Vits `input grid.

Control of .the conduction .of the sequencese'lec-- 3 .tor tubes .is derived from the keyboard TKB through the phantom-switch netWorkPlS, Where- .b,y., upon actuation of .anykey of thepos'itive .po-

tentials lare applied tothe ,properlsequence selector .keyboard KB corresponding to `a .code char-1V acter, .leads 36 tov gate `on the `appropriate .keyers to form the `corresponding codecharacter.

Thek eraser circuit In the operati-on ci fthe system 'described above,"

it will be apparent that vupon actuation 'of fa key fof the keyboard correspondingto a code charnoter requiring ygating on one for more keyer stages, the corresponding sequence selector or .selectors become conductive. Because of the 45 :normal operating characteristics of :gas discharge tubes this conductive condition persists feven after .termination of the transm'ission'of the node characters involved. If this Acondition were .permitted to continue, it will .be apparent that the Afollowing code character might not be :accurately transmitted, since the wrong sequence selec- Vfof a cathode resistor R515. The anode 0f the Leraser tube 3'! is connected through the Winding 'of the eraser relay ER. and resistor R'HS to the lead 2i, and thence through the eraser relay contacts 3S to the high positive potential source 33. The input grid of the eraser tube 30 is coupled to the cathodes of unit interval generator U'IGES by means of a Vcoupling condenser C503 and input resistor R5I4.

At the completion of the sequence of unit interval pulses, a positive pulse is produced at the cathodes of UIGIS which is transmitted to the eraser tube 3i) and triggers the tube 30 to render it conductive. This draws current throuehthe winding of the eraser krelay ERy and opens its contacts S8 to remove anode potential rom iead .www

0 comme, 4Uofi `5 A of .subsequent control '-'im'pulses' upon "their input fleadSS, @Theferasefrtube'l also automatically '.res'torl'es yi'tslf -tof theffprop'er condition Afor vper- .orrningfthe next erasing'function at the 'end of the .fllowirigcoding character, since Vby opening ownplatesupply and restores tube-k 31 Jto its non- .nonl'inctiv efcond-ition;V

. T 'finer/board sections "Theke-roeiersrisrepresents.the'poruen'rine apparatuswhi'cnis 'manipulated bythe operator, and is ;prfabIy-arranged in .a 'form Asimular to the standartypewriter keyb'oar'dfwith'rheadded `of the keyboard Aoperates a switch means which, 2" by virtue of thefphafntom-switch network PS,

'properly -fperates tthe unit interval generator 0 switch network must lfunction `to 'assuretwojcoi'rlrditions upon' depress-infr Aanyllzey: (1) 'Ihenunit'in'terv'lgenerator'chain mustjb'e yrstarted :atthe .proper-.generator to produce unit Llinterval pulses eqial number to thejle'ngth @(measured in unit intervals) of the code cha-i'- taeter represented lby the depressed key; 'and (2) The appropriate sequence selectors must l; be triggered on to provide' the correct `inni'lb'er f lpf dashes in the correct positions inthe chaiactel A 1,; L For these purposes, iamaX-imum of Ve separate 'triggeringY or initiating -pulses yis required A.for each character. On'e vtriggeringpulse -is neceslsary to initiate the'siequen'c'e of 'unit interval 5 pulses. Asinlcatei fabove this sequence `may require any odd number 'of 'unit t'ervapls'e's up to 19, depending upon the character being 5. sent, and 'accrdinglyt 'is necessary "for the keyboard and phantomeswitch network to be able 5,0 to apply this imitating purse 'te any 'one 'of teh points inl'tli iifnit generator cha-in, namely, the nine leads 29 (Fig. '3) YandY the input to UIGL Figure 2 illustrates Yfor 'each code 4character the particular generator to 'which the triggering pulse mustbe applied. 'In each case, this `is'tli'e generator havingthesame number as the interval preceding Athe rst mark in the character. `For example,fo r `A, `IZ-JIGI4A must be triggered; ifoffB, TGz' fo's'c, nids... ete. For zero 'and "beftriggeied, is also rator and sequence selector set. .o`1t below.

i set out fin'fgth .triggering ta e,

Inaddtiontdt 's'gle generator triggering .-piilse, upto frther pulses are necessary for triggering! appropriate l sed'uence selectors.

" 'As iind cated-1 above,y Aall odd-numbered unit terlpulss Aare directly passed by the corresponding odd-,numbered keyers to produce dot lfksi-vifthl'tpt. fWl'I1-Wl' avudash II/latlkH liS 70 desredgacording'to the .present invendmhe eve'r-'nulbredfk-" at the center interval o f the' three unit' 'intervals which form the dash narlsfgated "so, that the even-numbered Rester,passes'a'unitfinteval pulse also. ndr instances vthree successively numbered aecana l1' keyers pass unit interval pulses. The combination of these three unit interval pulses forms the dash mark.

As will be seen from Figure 2, dashes occur in various positions among the 19 intervals but gating only of even-numbered keyers is required by Virtue of the special convention by which the Morse code was set up, using single-unit dots and spaces and triple-unit dashes. The required gating of each of the even-numbered keyers is under the control of the corresponding even-numbered sequence selector. Examination of the code chart of Figure 2 will reveal that certain characters have no dashes whatever and hence require no gating. Other characters have from 1 to 5 dashes, requiring up to ve keyers to be gated and correspondingly requiring up to 5 sequence selectors to be triggered. The particular requirements for the complete Morse code are shown in the following generator and sequence selector triggering table, listing opposite each code character the numbers of the sequence selectors to be triggered and the number of the Sequence Selectors UIG to be Code Character To Be Triggered Triggered From this table it will be seen that each character has a specific combination of sequence selectors which must be triggered. Thus, for A, sequence selector I8 must be triggered; for B, selector I2; for Y, selectors 8, I4 and I8; for zero, selectors 2, 6, I0, I4 and I8. To be triggered, each of these sequence selectors must have a positive voltage pulse applied to its input lead 36, from the keyboard KB and phantomswitch network PS.

One manner in which this requirement can be met is by the use of six-pole single throw switches individually actuated by respective buttons of the keyboard. One set of contacts of such six-pole switches is assigned to trigger the proper unit interval generator. For this purpose,one contact of each pair is connected to a y positlve potential source, and the other contact lated resistors may be connected individually to such contacts.

Similarly, the remaining contact sets for each character switch may be connected to the proper ones of the 9 sequence selector inputs, as indicated by the above triggering chart. However, when this is done a number of problems arise, among which the most important is the v fact that the resulting network provides a number oi shunt paths which either triggerlng potential to undesired sequence selectors or lso reduce the resistance of its input circuit as to prevent triggering of the desired sequence selector. Furthermore, considerable mechanical diiiculty and complexity is experienced in mounting some 44 six-pole switches in as compressed a space as is taken by a conventional typewriter keyboard.

These disadvantages are overcome by the present invention, which further provides a greatly improved type of network suitable for the requirements of this system, in which each character key of the keyboard need actuate but a single-pole single-throw momentary contact switch, which is easily mechanically realizable in the conned space available. At the same time the problems incident to back coupling or shunt paths are eliminated. In effect, the phantom-switch network PS permits a single-pole switch to serve the function of a multipole switch in turning on several circuits.

The phantom-switch network PS of the present invention will be more readily understandable by reference to Figure 4, illustrating the manner in which this phantom-switch network PS is built up. For clarity, this figure shows only three representative character keys l, C and Z on the keyboard, but it will be understood that the remaining 41 keys are connected in accordance with the principles to be described.

Each key of the keyboard is directly connected mechanically to a single-pole switch. The switch corresponding to the character I is indicated schematically by the reference numeral itl; the switch corresponding to the letter Z by H32; and the switch corresponding to the letter C by |93. Each of these switches has one terminal connected directly to a suitable source of positive potential |04, which may be the same as source 23 or 33 of Figure 3. The other terminal of switch mi is connected through an isolating resistor H also serving as a voltage dropping resistor to the appropriate unit interval generator. From the triggering table above, it will he seen that for the digit 1 the unit interval generator 2 must be fed the triggering pulse and accordingly resistor il I is connected to the cathodcs of unit interval generator 2. Similarly Z-switch t2 is connected through a similar resistor Iz. to its appropriate unit generator which is here No. C-

`switch I3 is connected through a similar resister `I I3 to its unit interval generator which will be seen to be also No. 3. The parallel connection of C-switch ii and Z-switcn EEZ- to the same unit interval generator' has no effect on the system, since only one or" these switches is `closed at any one time and by the means herein- 13 ,below described, no paths to ground or-.to the negative .potential terminal from the other switches which are open are present. It will loe @understood that .each of the remaining fil character switches is connected through its individual isolating and voltage dropping resistor to its proper unit interval generator illustrated in the vtable above. Y

Reference to Figure 2 will show that the code symbol for digit 1 is formed by one dot and four dashes. This immediately indicates that four sequence selectors must be triggeredrto gate on four appropriate keyers. Figure 2 shows'that the center intervals of these four dashes are nurn- Ybered 6, I0, 14 and 18. Accordingly, sequence selectors numbered 6, 10, 14 and 18 must be triggered,4 asis indicated on the triggering table hereinabove. For this lpurpose the .terminal cf switch [Ill `is connected through'respective isolating elements I I4, II5, IIS and il? to respective Vvoltage dropping resistors IIB, IIS, |20 and I2! and then tothe respective input circuits sequence selectors 5,- I Il, I4, and I8. 'Ihe manner in which such connection Ais made is illustrated inthe case of sequence selector IS, showing its input resistor 'R408 and its cathode resistor Rtii.

The isolating elements IIe may be unidirect-iona'lly' conductive elements such as crystal rectiers or germanium diodes, or may be neon or A suitable and preferred element has been found -to be a neon buib of the `lNE2I type. The voltage of source Ili is chosen to have a sufcient value and magnitude so as to -fcause conduction ofthe neon bulbs lili to I Il.

The isolating resistors IIB to 12| in association withfsequence selector input resistors Rite provide voltage dividers which apply appropriate triggering potentials to the sequence selectors 5, t0, I4 and I8, as desired. Y

- Reference to Figure 2 and the above triggering table shows that the character Z is formed by two dashes and two dots, requiring gating on of the keyers IU and It and consequent triggering vvof selectors |0 and I-t. Accordingly, the terminal of the Z-switch IGZ is connected through isolating element |22 and resistor |23 to they input o! sequenceselector It, and through isolating relement |24 and resistor |25 to theAinput'o-i sequence selector i4, and operates similarlyy to gate ori-the proper Vsequence selectors for this charf acter. Similarly, the code character C is formed 'by two dashes and two dots, requiring gating on keyers I0 and Iii, which is done by the connection of the terminal of C`-suntch |'3 to sequence selector I8 by way oi isolating element |2e, resister |21 and to sequence seiector i5 by isciat in" element, His and resistor V23.

The remaining .characters of the keyboard are connected to their respective sequence selectors indicated on the triggering table above in the ,y `same manner, with individual isolating elements and connecting voltage dropping resistors.

VItY will. be apparent that stray shunt paths and .backvoltages are prevented by this system. For

example, referring to Figure e, three separate l;

both neon bulbs I I5 and Il 6 whichremaln ropencircuited and hence isolate the undesiredy sequence .selector I4 from the system. Similarly, other sequence selectors are isolated and only thedesired selector can be triggered. vIn this' Way, the e'iectsof the remaining connections not directly utilized or desired are eliminated and only the desired sequence selectors are actuated.

.Monitor Lcircuit r In many applicationsof the present system, it is desirable to be able tolisten to the code transmission being produced.. This is not only useful v-for monitoring purposes, and to assure that .the speed control is .set sunicientjly high to avoid overlap of characters at the normal typing "speed, but is also extremely useful in assisting in instruction of Morse code." By a monitor circuit such as the one now to be described, itis possible for an operator .to produce Morse code Without any knowledge whatever vof what the code may be; merely by pressing a Vparticular letter or digit of the keyboard, the Morse code character is automatically produced `and heard. l This pro- 'vides a simple and ready means to learn Morse ncoole by actual aural practice.

QFor this purpose, a monitor circuit M is provided, which, asV shown in Figure 3, essentially consists of a phase shift oscillator formed by a triode or other type o f tube 4I .having its anode coupled to its input grid Vby aphase .shift network 5I.

The anode is also ,coupled to a high positive potential source, which may be source 33, in series with a jack J. The cathode is coupled to a low positive potential source such as 23, or to negative terminal I4, through a cathode biasing resistor R632 which normally maintains the tube AM cut off. The circuit thus provides ka tone oscillator of a frequency of' approximately 1,000 `cycles or other desired value.

' The grid of monitor tube 4I is coupled to the cathodes of' the keyer tubes KI to KIQ. In this way the normally blocked monitor oscillator M is unblocked by the pulses forming the code character as supplied to the keying relayKR, and a Vsuitable reproducer coupled tothe jack J permits listening to the code transmission produced. The present invention also includes means for 'checking operation of the circuit at any time. On the keyboard thereis provided a "clear or 'CL key, which operatesto trigger the ilrst unit interval generator, without operating any of vthe sequence selectors. If. all unit generators are operating satisfactorily, a, sequence of ten dots Will be produced, which can be heard by 'means of the monitor circuit. Any trouble will be detected by the non-appearance of one or more of these dots, the position of the rmissing rdot being indicative of the defective generator stage.

' l While vthe present invention has been described las applied tothe International Morse code, it lwill be understood that it may be used with any type of code, either with code characters of equal length or of unequal length. In any "code, the

'code characters may be broken down into unitv 'intervals'.` In general, the number of unit interval generators is equal to N, the number of intervals in the longest character. In the most general case, each generator may initiate the pulse sequence,v and is provided with a control lead such as 29 in Fig. 3; As many keyers are iused as there are generators. As many sequence selectors are used as necessary to obtain all code assai 1c 15 ,A Y characters; in the most general case, there will also be N.

Where all codeicharacters are of equal length, all leads 29 are omitted, and the full pulse sequence is generated for each character. ln particular, for the teletype code, using ve unit intervals, any one of which may be either a space or a mark, ve unit interval generators, ve keyers and ve sequence selectors are used. Once the code is set forth in the manner of Figure 2, the sequence selector triggering chart is easily read oiT, and leads directly tothe connections loetween the keyboard switches and the selectors, following the principles already given.

It will be understood that the present invention is not limited to the speciic circuits shown. Many types of single-pulse or univibrator circuit are known, and any circuit capable of producing the unit interval pulse sequence of selective total length may be employed. Similarly, the keyer circuits shown are one form of the general type of circuit known as gating c` cuits, and many equivalent gating circuits capable of performing the same functions may be substituted. Also, the specic sequence selector circuits described represent but one out of many types of circuit suitable for properly controlling the keyers, and others may be used in the present system.

Accordingly, the present invention is notV to be deemed limited by the above description, which is solely illustrative, since many other types of circuit may be used in place of those described herein, and the invention is dened only by the claims granted to me.

What is claimed is:

l. A keyboard-operated code producer for International Morse code, comprising a keyboard having a plurality of keys each corresponding 'to one character of said code, a, like plurality of normally open single pole momentary Contact switches mechanically coupled respectively to said keys to be actuated thereby, each of said switches having iirst and second terminals, a source of direct potential coupled to all said rst terminals, a lil-stage uni-pulse generator chain having nineteen cascaded generators, each of said generators loe-ing adapted in response to receipt of a trigger pulse to produce a single output rectangular pulse and to supply a trigger pulse to the next generator of said chain coincidentally with the termination of its own rectangular pulse to thereby trigger said next generator in similar manner to produce a further output pulse and a further trigger pulse for the following generator, all said output pulses having uniform duration, whereby application of a trigger pulse to any generator of said chain produces a sequence ci output uniform-duration rectangular' pulses equal in number to the number of generators from the generator first triggered to the end of said chain, the second terminal of each ley switch being coupled t0 the input o that one of said generators from which to the end of said chain there are as many gencraters as there are unit intervals in the character corresponding to said key, whereby upon depressing said key to close its respective switch, a trigger pulse is applied to the appropriate point of said generator chain to initiate a sequence of output pulses equal in number to the intervallength of the respective character, nineteen keyer circuits, each of said generators having its output coupled to the input of a respective keyer circuit to supply its respective output rectangular pulse thereto, a keying relay having a pair oi' output contacts and a winding, the outputs of all said keyer circuits being connected in parallel to said keying relay winding whereby said contacts are operated in correspondence with pulses passing individually through said keyer circuits, nine sequence selector circuits coupled to the nine even-numbered keyer circuits, each being adapted upon excitation by a contact pulse to gate-on its respective keyer circuit, and means coupling the second terminal or each of said key switches to those of said sequence selector. circuits corresponding to keyers whose input pulses from said generator chain have interval positions corresponding to the positions of the center intervals of the dash marks of the character corresponding to said each key, whereby upon actuation of any key oi said keyboard, said generator produces a sequence of pulses of number equal to the interval length of the code characer corresponding to said actuated key, and said keyers pass to said keying relay only those pulses corresponding to dots and dashes of said code character.

2. A keyboard-operated code producer for a telegraphic code of the mark and space type whose code characters are of diierent numbers of unit intervals in length, comprising a keyboard having a plurality of keys each corresponding to one character of said code, a like plurality of normally open single pole momentary contact switches mechanically coupled respectively to said keys to be actuated thereby, each of said switches having rst and second terminals, a. source of direct potential coupled to all said first terminals, a plural-stage uni-pulse generator chain having a number of cascaded generators equal to the number of unit intervals in the longest character of said code, each of said generators being adapted in response to receipt of a to any generator of said chain produces a sef quence of output uniform-duration rectangular pulses equal in number to the number of generators from the generator rst triggered to the end of said chain, the second terminal of each key switch being coupled tot he input of that one of said generators from which'to the end of said chain there are as many generators 'as there are unit intervals in the character corresponding to said key, whereby upon depressing said key to close its respective switch, a trigger pulse is applied to the appropriate point of said generator chain to initiate a sequence of output pulses equal in number to the interval length of the respective character, a pluralityof keyer circuits equal in number to the number of said generators, each of said generators having its output coupled t0 the input of a respective keyer circult to supply its respective output rectangular pulse thereto, a keying relay having a pair of output contacts and a. winding, the outputs of all said keyer circuits being' connectedV in parallel to said keying relay winding whereby said contacts are operated in correspondence with pulses passing individually vthrough said keyer clrcuits, a plurality of sequence selector circuits 17 coupled to respective ones of said keyer circuits, each being adapted upon excitation by a contact pulse to gate-on its respective keyer circuit, and means coupling the second terminal of each of said key switches to appropriate ones of said sequence selector circuits to apply control pulses from said source thereto upon actuating any one of said keys to cause'said keyer circuits to pass only those of said sequence pulses required to form the code character corresponding to said 10 actuated key, whereby said keying relay winding is energized by a sequence of pulses having duration and spacing corresponding to said code character.

NATHANIEL G. A. DORFMAN.

References Cited in the le of this patent Number Number UNITED STATES PATENTS Name Date Jones Dec. 22, 1908 Saunders May 8, 1934 Compton Apr. 2,3, 1946 Dickinson July 4, 1950 Krause et a1 Sept. 18, 1951 Baker Sept, 30, 1952 FOREIGN PATENTS Country Date Great Britain Jan. 31, 1939 

